Recoverable sleeve assembly for pipe joint

ABSTRACT

A method of covering two or more joined pipes which are to be pulled through soil is described. The two coated pipes are bared of coating or order to join them. The bared region is covered with a first heat shrinkable sleeve, and then a second heat shrinkable sleeve is applied to overlap the first sleeve and extend beyond it in the direction of the leading edge of the joined pipes. A metal band is secured around the second sleeve at the leading edge.

This invention relates to a covering for protecting a joint betweenpipes when the joined pipes are to be pushed or pulled through soil.

Where pipelines are to be positioned under a road or river it is notpractical to dig a trench to bury the pipe. Two main techniques aregenerally used for positioning the pipe. In the first technique, knownas directional drilling, a non-linear hole is drilled under the road orriver, and the hole is filled with a special liquid to stop the soilcollapsing into the hole. In the second technique there is nopre-drilling and the pipes are simply pushed into the soil, each lengthof pipe being joined and pushed into position on site.

The pipelines which are used in the above techniques are typically steelpipes coated with a corrosion protective layer. The corrosion protectivelayer may comprise a sintered polyethylene mil coating. Alsoincreasingly popular are multi layer coatings comprising sequentially afusion bonded epoxy layer, a hot melt adhesive layer and an outerpolyethylene layer. The protective coating is typically 1.5 to 9 mmthick. The pipes are generally joined by welding, and the protectivecoating is removed to bare the underlying steel in the joint region toallow the weld to be made. This region is therefore open to theatmosphere and must be recovered, for corrosion protection, before thejoined pipes are buried in the soil.

There are a number of existing solutions for recovering the bared jointof the steel pipes. One solution involves sintering polyethylenematerial in a mold positioned around the joint, thereby reformulatingthe mil coating around the joint. Another solution involves priming thepipe then wrapping an epoxy coated glass fibre wrap around the pipejoint and curing the epoxy. A third solution involves a triple layerrecoverable sleeve positioned over the joint region again with an epoxyprimer on the outside. All these solutions are operator-sensitive andtime consuming. Particularly where the pipes are to be joined on sitethis is particularly disadvantageous, and in some instances only onepipe length per day can be added.

Also in some of the prior art, e.g. using the triple layer recoverablesleeve and epoxy outer jacket, the leading edge of the covering is proneto fraying as pipeline is pulled or pushed through the soil on the pipecovering.

Some effort has been expended to try to decrease the profile of thecovering at the joint region in order to minimize the fraying at theleading edge. However we have discovered that even though it increasesthe profile at the leading edge, an effective corrosion protectivecovering can be positioned around the joint which resists leading edgefraying by using a band, made for example from a metal, from acomposite, or from an engineering plastic, the band being tightenedaround a combination of recoverable sleeves. Therefore a first aspect ofthe invention provides a method of covering a joint between two coatedpipes the coating of which has been bared in the joint region, and whichpipes are to be pushed or pulled through soil, the method comprising:

(i) recovering a first heat recoverable sleeve around the joint region,to cover the bared joint and to overlap the coating on either side ofthe joint region;

(ii) recovering a second heat recoverable sleeve to overlap the firstsleeve and to extend beyond the first sleeve in a direction towards theleading edge of the pipe joint; and

(iii) fastening a band around the second sleeve at the leading edge ofthe sleeve.

Preferably the second heat recoverable sleeve is thinner than the firstheat recoverable sleeve. This means that when the band is fastenedaround the second sleeve there is a small step down from the sleeve tothe pipe surface. Typically the first sleeve is at least 2 mm,preferably 3 mm, generally about 4 mm thick. In contrast the secondsleeve is typically less than 2 mm preferably about 1 mm thick. The bandis preferably 0.3 to 1.5 mm thick, typically about 0.8 mm thick.

While the double sleeve combination is preferred, it is possible toattach the band directly over the first sleeve, not using a secondsleeve.

Thus, a second aspect of the invention provides a method of covering ajoint between two coated pipes, the coating of which has been bared inthe joint region, and which pipes are to be pushed or pulled throughsoil, the method comprising

(i) recovering a first heat recoverable sleeve around the joint region,to cover the bared joint and to overlap the coating on either side ofthe joint region; and

(ii) fastening a band around the first sleeve at the leading edge of thesleeve.

A third aspect of the invention provides an assembly which can be pulledor pushed through soil, comprising:

(i) two coated pipes which have been bared of coating and joined in abutting relationship;

(ii) a first heat recoverable sleeve recovered around the bared jointregion to cover the bared joint and to overlap the coating on the pipeson either side of the joint;

(iii) a second heat recoverable sleeve recovered onto the first sleeveto overlap the first sleeve and to extend beyond the first sleeve in adirection towards the leading edge of the pipes; and

(iv) a band fastened around the second sleeve at the leading edge of thesleeve.

A fourth aspect of the invention provides an assembly which can bepulled or pushed through soil, comprising:

(i) two coated pipes which have been bared of coating and joined in abutting relationship;

(ii) a first heat recoverable sleeve recovered around the bared jointregion to cover the bared joint and to overlap the coating on the pipeson either side of the joint; and

(iii) a band fastened around the first sleeve at the leading edge of thesleeve.

A heat recoverable article is one whose dimensional configuration may bemade to change when subjected to an appropriate treatment. Usually thesearticles recover, on heating, towards an orginal shape from which theyhave previously been deformed, but the term "heat-recoverable" as usedherein also includes an article which, on heating, adopts a newconfiguration, even if it has not been previously deformed. Referencemay be made for example to U.S. Pat. No. 2,027,962, U.S. Pat. No.3,086,242, U.S. Pat. No. 3,597,372, U.S. Pat. No. 2,027,962, GB 1440524.

The first heat recoverable sleeve extends over the whole of the baredportion of the joined pipes and slightly overlaps the protective coatingon the pipes (e.g. the mil coating on steel pipes). The secondrecoverable sleeve extends over the first sleeve in a direction towardsthe leading edge of the pipe joint. (By leading edge is meant the edgeof the joint which leads when the pipeline is pulled or pushed into thesoil). The leading edge of the second recoverable sleeve is subject toabrasion as the pipeline is pulled through the soil. Thus the metal bandis tightened around this leading edge. Both sleeves are preferably linedwith an adhesive, preferably a heat activatable adhesive (e.g. ahot-melt adhesive), which is activated on recovery of the sleeves.

One or both of the sleeves may comprise a heat recoverable fabric. Heatrecoverable fabrics are known and described, for example, in EP-A0116393 (MP790) and in EP-A- 0117026 (RK176).

The band may (1) comprise any material having an appropriate elasticmodulus, and (2) having an appropriate thickness such that it can betightened around the sleeves, as described below, for example to atension of 10 000N. As a preferred example, the band may comprise ametal, for example steel, a composite, for example a carbon fibrelaminate, or an engineering plastic.

The band must be tightened around the leading edge of the arrangementwith a tension sufficiently high that it substantially prevents frayingof the leading edge when the pipeline is pulled, or pushed through thesoil. We have found that surprisingly this can be achieved withoutdamaging the protective coating on the pipe, typically the mil coatingon steel pipes.

After the band has been tensioned and released the amount of elasticenergy stored in the band (if any) is not so high as to force the bandthrough the sleeve(s) and mil coating. This ensures that the band isalways separated from the pipe by the sleeves and/or mil coating. Thisis particularly important where the band comprises a metal.

A test was devised to measure the force required to deflect or fray theleading edge of the system. The test apparatus for the test is shown inFIG. 1. A steel pipe 2 has a mil coating 4. A recoverable sleeve/metalband assembly 8 (not shown in detail) covers the mil coating. Aspecially calibrated plate 10 is pushed over the steel pipe/mil coating,and the force to deflect the recoverable sleeve/metal band assemblymeasured. FIG. 2 is a graph showing the deflection force vs thedisplacement (deflection). The graph is for a metal band tightened to atension of 10000N around a pipe of diameter 16 inches. Curve (1) is forthe assembly shown in FIG. 1. (The dip in the curve corresponds to theinitial movement of the metal band to abut against the first sleeve ofthe assembly 8. This initial movement will typically occur in thepreferred arrangement using first and second sleeves. Where the firstsleeve is thicker, it is not possible precisely to position the metalband over the second sleeve to abut the end of the thicker first sleeve.Typically the band is positioned a small distance away form the firstsleeve, and moves initially until it abuts the first sleeve). It can beseen that there is a significant displacement for forces of greater than2, even greater than 4 tons. Curve (2) which is dotted is a comparativecurve showing the force vs displacement when plate 10 is forced directlyagainst the mil coating 6, on the pipe with no sleeve/metal bandassembly 8. It can be seen that for forces up to about 4 tons the curvesfollow similar paths, indicating that the sleeve/metal band assembly isas resistant to displacement as the mil coating. Typically the metalband may be exposed to forces of about 1.5-2 tons as a pipe ispulled/pushed through soil.

FIG. 3 shows the radial pressure in bar/cm² exerted on a pipe of variousdiameters by a metal band tightened to 10000N. It can be seen that thepressure is less than 10 bar/cm² on a 40 inch pipe but greater than 20bar/cm² on a 16 inch pipe. Preferably the band is tensioned according tothe pipe diameter so that it does not significantly damage mil coating.The tension required is a function of the pipe diameter.

Preferably the metal band comprises steel material. It is preferably0.6-1 mm, typically 0.8 mm thick, and 0.8-1.2, typically 1 inch wide.

The first recoverable sleeve preferably has a thickness of 2-6 mm,typically 4 mm, and is of length sufficient to overlap the pipe coatingon either side of the joint by at least 80, especially at least 100 mm.The second recoverable sleeve preferably has a thickness of 0.6-1 mm,typically 0.8 mm, and overlaps the first sleeve by at least 20,preferably at least 40 mm and the pipe coating by the same amount.

Referring to FIG. 4, steel pipes 20, 22 are welded at line 24. Each pipe22, 24 is coated with a mil coating 26. The coating 26 has been removedaround the weld line 24. A first heat recoverable sleeve 30 overlies thebared region and overlaps the mil coating 26 on either side of the baredregion. The leading edge of the joined pipes is to the left of thedrawings (i.e. the pipes move from right to left when pulled/pushed inthe ground). Heat recoverable sleeve 32 overlaps sleeve 30 and alsoextends beyond sleeve 30 over the mil coating 26 in the direction of theleading edge. Metal band 34 is positioned at the leading edge of sleeve32. For installation sleeve 30 is recovered, then sleeve 32 (e.g. with agas torch or hot air gun or electrically). Then metal ring 34 isinstalled and tightened to an appropriate tension as determined by thediameter of the pipes.

I claim:
 1. A method of covering a joint between two coated pipes thecoating of which has been bared in the joint region, and which pipes areto be pushed or pulled through soil so that, in use, the pipe joint hasa leading and a trailing edge, the method including the use of a firstheat recoverable sleeve and a second heat recoverable sleeve, and themethod comprising the steps of:(i) positioning the first heatrecoverable sleeve around the joint region so that it covers the baredjoint and overlaps the coating on either side of the joint region; (ii)heating the first heat recoverable sleeve to cause it to recover intocontact with the bared joint and with the coating on either side of thejoint region; (iii) positioning the second heat recoverable sleevearound the first sleeve and the pipe coating on at least one side of thefirst sleeve which side, in use, will be towards the leading edge of thepipe joint, so that the second sleeve overlaps at least part of thefirst sleeve and at least part of the said coating on the said at leastone side of the first sleeve; (iv) heating the second heat recoverablesleeve to cause it to recover into contact with (a) the first sleeve and(b) the said pipe coating on at least one side of the sleeve after theheating of the first heat recoverable sleeve; and (v) fastening a bandaround the second sleeve at the edge of the sleeve which, in use, istowards the leading edge of the pipe joint.
 2. A method according toclaim 1, wherein the band is fastened to a tension that is high enoughto prevent fraying of the second sleeve as the pipes are pushed orpulled through the soil, but that is low enough not to damage completelythe underlying coating on the pipes.
 3. A method according to claim 1,wherein either or both the first and second heat recoverable sleevescomprise heat shrinkable fibers.
 4. A method according to claim 1wherein the band comprises a metal.
 5. A method according to claim 1,wherein the first and second sleeves are lined with adhesive.
 6. Anassembly which can be pulled or pushed in use through the soil,comprising;(i) two coated pipes which have been bared of coating andjoined in a butting relationship to form a pipe joint, the pipe joint,in use, having a leading edge and a trailing edge when pushed or pulledthrough the soil; (ii) a first sleeve positioned around the bared jointregion so that it covers the bared joint and overlaps the coating on thepipes on either side of the joint; (iii) a second sleeve positioned sothat it overlaps at least part of the first sleeve and extends beyondthe first sleeve in a direction towards the leading edge of the pipejoint; and (iv) a band fastened around the second sleeve at the edge ofthe sleeve which, in use, is towards the leading edge of the pipejoint,wherein (a) the first sleeve has been so positioned by firstplacing a first heat recoverable sleeve around the bared pipe joint andthe coating on either side thereof, then heating the first recoverablesleeve to cause it to recover and (b) the second sleeve has been sopositioned by then placing a second heat recoverable sleeve so that itoverlaps at least part of the first sleeve and extends beyond the firstsleeve in the said direction, and then heating the second recoverablesleeve to cause it to recover.
 7. An assembly according to claim 6,wherein the band comprises a metal.
 8. An assembly according to claim 6,wherein the first and second sleeves are lined with adhesive.
 9. Amethod of covering a joint between two coated pipes, the coating ofwhich has been bared in the joint region, and which pipes are to bepushed or pulled through soil so that, in use, the pipe joint has aleading and a trailing edge, the method including the use of a firstsleeve which is heat recoverable, and comprising the steps of:(i)positioning the first heat recoverable sleeve around the joint region,so that it covers the bared joint and overlaps the coating on eitherside of the joint region; (ii) heating the first heat recoverable sleeveto cause it to recover into contact with the bared joint and with thecoating on either side of the joint region; and (iii) fastening a bandaround the first sleeve at the edge of the sleeve which, in use, istowards the leading edge of the pipe joint.
 10. A method according toclaim 9, wherein the band comprises a metal.
 11. A method according toclaim 9, wherein the first sleeve is lined with adhesive.
 12. Anassembly which can be pulled or pushed in use through the soil,comprising;(i) two coated pipes which have been bared of coating andjoined in a butting relationship to form a pipe joint, the pipe joint,in use, having a leading edge and a trailing edge when pushed or pulledthrough the soil; (ii) a first sleeve positioned around the bared jointregion so that it covers the bared joint and overlaps the coating on thepipes on either side of the joint; and (iii) a band fastened around thefirst sleeve at the edge of the sleeve which, in use, is towards theleading edge of the pipe joint,wherein the first sleeve has been sopositioned by placing a first heat recoverable sleeve around the baredpipe joint and then heating the first recoverable sleeve to cause it torecover.
 13. An assembly according to claim 12 wherein the bandcomprises a metal.
 14. An assembly according to claim 12, wherein thefirst sleeve is lined with adhesive.